Bowden Belt Extruder

Yet another "Extruder", yup ?*

*(we'd rather say feeder)

So true ! But this one is an anwser to a bunch of issues. My Bowden Belt Extruder, has required about 3 months of single work, then with the help of maker friends, 9 months was used for beta testing and overall adjustments. This is not a remake : it was engineered considering the expected specifications form start to end.

I started to 3d print several years ago and I've been used up to 100 lbs filament yet. I owned, designed and builded several printers, and encountered a lot of issues from one to another. My bowden belt extruder try to avoid most of commun issues and adds interesting features too. Maybe my extruder is not the best ever, but it probably stand close to most interesting ones. It's just one vision of what a good extruder must be.

If you plan to build your first printer, you'll probably in search of the best possible parts. Otherhand, if you own one, you 3d printer was already provided with a feeder. But, even if you never encountered any issue with it, you can think about an upgrade to improve print quality or get better features.

Design choices and why ?

Why the bowden technology ? For newbies, bowden means the feeder is distant from the printhead. The filament is carried thru a PTFE tube which makes a bow => bowden. By removing the feeding motor and parts from the printhead, you get a lightweight printhead. As printhead moves can be very quick on a 3d printer with a lot of direction changes, extra weight brings more vibrations and have a real influence on print quality. This is particulary pregnant if the other components are not totaly stiff or playless. Most critics about bowden comes about you could not print flexible materials with a bowden setup. Well, actualy, this is not totaly true. I print pretty decent flexible parts with my bowden setup. I see no difference compared to direct drive extruders. I can say why. Most of bowden kits are provided with one meter (3 ft) of bowden tube. And people use all the available lenght. It's a mistake. You want to keep the bowden distance as short as possible. As the maximum run of a printhead is usualy about 200mm, you should not need over 300mm to keep it moving freely. Otherhand, flexible filaments should not be printed too fast. It's important for a good bond between layers and a good overall print quality. If a bowden feeder is properly designed and if it uses a shorten bow tube, then a bowden setups have some advantages and no cons.

Why a greared extruder ? Easy awnser ! This gives extra power to the feeder and it brings more resolution to the extrusion. My bowden belt extruder brings 4 times more torque and precision compares to a direct drive feeder.

Why a belt extruder ? Most motor reductions use gears, mostly printed of course, and gears are noisy. Seccond, the belt can be tensioned with precision so it have no play, and there's mostly no wear so it's durable.

What makes it interesting ?

Perfect path : the filament is driven constantly since out of the gear, no possible filament jam

Uses the MK7 hobbed gear, the best on the market actualy (better than MK8).

Low cost.

Easy building.

Step 1: Bill of Materials

If you want to build your own Bowden Belt Extrudeur, you will need a set of printed parts available on thingiverse (Thing#1579394). If you don't own a printer yet, you can order prints directly on Thingiverse, otherwise there's different ways to get printed parts : request to a friend/maker with a 3d printer, ask at the nearest fablab, or order directly on 3Dhubs or Thingiverse. Note serious provider will send debured parts.

Two version of the printed parts are available. One with the regular marking, and one with unshown marking. Use whatever you like. You can visit my website for further details and the article in french : www.j-max.fr

Hardware :

You can order the hardware at any provider. All the hardware in use are commun standard parts. Usualy best price can be found on Aliexpress.com or Ebay. Just take your time and compare to be sure to get exactly the right part at the right price.

J-Max, first of all, thanks for this design! I've seen a lot of extruders, and when I saw yours I decided I simply have to try it out, so I'm building two of them right now for a new dual-extrusion printer I'm building (a D-bot).

My question: you mentioned that the stepper should be at least 37mm long. I didn't see this before I ordered my steppers, and I ordered short body steppers with around 20mm long bodies. I bought them because they were the same ones recommended for the E3D Titan geared extruder, on the basis that the gear reduction makes it unnecessary to have normal high torque steppers for the extruder.

What's the basis for your recommendation of a minimum 37mm stepper size? Have you actually tried your extruder with a short body stepper?

Well, I'm not into E3D's process, but we may consider the Titan is a light weight extruder, so it should be interesting in direct drive applications. In this purpose, the motor should be light weight too. Through, I don't know if the Titan's small gears can stand a lot of torque.

My design is a long time development (for an individual) followed by more than 6 months beta testing by a 4 people team on various printers. We did it seriously. The main goals was quietness, quality and ease of use. That means no fail, whatever you may ask. With smaller motors, we experienced unconsistency of filament deposit on faster printers or low melting temperature filaments. Filaments with fibers also need extra torque. We did not wanted a setup at minimal, so a comfortable security margin was applied to print properly and cover any possible issue. With at last a 37mm long motor you can be confident, whatever your setup or settings : silent motor drivers (which provide less torque), overheating on long prints, hard core delta printer's speed, and so on. Just like we did : install it and forget it :)

Probably you can make it work with 20mm motors, but stay in reasonable expectations because you won't have extra torque to stand any situation. Stick to 16 microsteps, and don't print fast with exotic filaments.

On my setups, I use 17HS8401 motors (48mm). There's no huge difference on the price tag and the motor will never be to blame.

J-Max,Thanks for your response! The Titan extruder has a 3:1 reduction ratio, which of course is even less than your 4:1 ratio, so if the short steppers work for that extruder, I would think it would work well for yours too. That being said, I recognize that you speak here with the voice of experience, and it would be foolish of me to think I know better just because something makes sense in my mind.

I've therefore ordered a pair of 40mm steppers to use instead of the 20mm ones I'll be receiving tomorrow (I'll save those for future projects). I'll be very happy knowing that my extruders will work well with no question as to whether there's enough torque for any given situation they may face. I do in fact plan to use exotic filaments with carbon fiber, metal fillers, etc., and so I want to make sure I've got the most sensible setup I can have.

Two questions:1. I was always told to be careful moving steppers by hand because the generated voltage might damage the electronics, so I'd hesitate feeding 300mm by hand cranking. Is this no issue in your opinion? I suppose your electronics are still alive after months of testing, but better safe than sorry :)2. Would it be easy to give this a smaller advantage than 1:4 by just using a bigger pulley on the motor (I'm not as much concerned about force than retraction speed), or do I overlook something? If yes this would make your design even more versatile :)

You're absolutely right about the current generation. Otherhand, it's only a small amount of current generated. You could barely light up a led. You don't need a big motor, so the smaller it is, the less current is generated. I choosed to don't take the current generation in consideration, and it's true, any of my printers still work fine, even if I change filaments frequently. So do the beta tester's. As far as I know, they all kept it. But I understand you can be afraid about that. There's two solutions for you. First, the radial instert of the motor can help you. You just have to loose 3 screws and disengage the motor. You just slow down the operation by 10 to 15s if you leave a hex driver near the extruder. Another permanent solution could be inserting a circuit with some diodes and a discharge protection, somewhere between the motor's wires. To me, it over complicates something that works well. I used to find a design good when there's nothing left to remove. I'm not into any additive design process. The simpler, the better IMHO.

About the bigger pulley. My design is only a way to manage the feeding, whatever the care I put into it, it won't be universal anyways. The leading ideas was (in order) : practical, quiet, compact. By pratical I wanted to solve commun problems for the user, like unnecessary time consuming operations, lack of precision or torque, easy maintenance, wear problems. First, the gear size is also in close relationship with the belt and the shaft distance. Obviously it's not a single gear, it's a whole system. About pulleys, usualy, the smaller, the better. As the motor gear grows you reduce the torque which is dependent of the radial distance to the shaft centre. So, the system will be less efficient even if you enlarge the output pulley to keep the ratio unchanged. Then, if diameter of the pulleys changes, you need to raise the shafts linear distance to leave enough space for the radial insert tensioning system. Take in consideration that you will have also the belt factor to manage : size (which grows quicky, enlarging shaft distance, and its avalaibility. Plastic have also one big problem : it's not a very stiff material. If you enlarge, you need to make your housings thicker. So, as you can see, there's more disavantages to grow big.

But I understand your consideration was much about retractation speed. And you're right, a fast retractation helps a lot to reduce the printing time. Between 16 to 20 tooth, you only get potentialy 20% more speed. Meanwhile, you loose some torque too. We know the speed of a motor, especialy in short moves, is dependent of the acceleration settings. The more torque you have, the quicker acceleration you can ask. There's calculation to do, but guess a differential of 4 tooth does not bring any significant speed difference. Actualy, the retractation speed with my bowden belt extruder is near 200% faster than on my previous Wade's. Note we never tryed to push the acceleration rate to the maximum (I put it in the to do list) but here I'm at 5m.s which is pretty quick.

Well, when you buy a cheap kit, you probably start to improve it with better printed parts. You're right. But if you sourced good parts or bought a nice printer since the sart, then you'll probably find it usefull in many other tasks. Whatever is your centre of interest.

You're right for the flat side of the shaft. Especialy if your MK7 have only one screw to lock on to the shaft. It's a shame but I was not brave enough to film a new video !

I had started with an own build of a printer from scratch. So I definitely have to replace some of the wooden parts by prints. Unfortunately I have more delays than improvements at the moment. Movement is working but heating is something I have to tackle next.